Archerfish have demonstrated their ability to distinguish between different human faces - by spitting at them!

The research, carried out by a team of scientists from the University of Oxford (UK) and the University of Queensland (Australia), found that archerfish were able to learn and recognise faces with a high degree of accuracy – an impressive feat, given this task requires sophisticated visual recognition capabilities.

It is the first time that fish have demonstrated this ability. Dr Cait Newport, of the Department of Zoology at Oxford University, said: “Being able to distinguish between a large number of human faces is a surprisingly difficult task, mainly due to the fact that all human faces share the same basic features. All faces have two eyes above a nose and mouth, therefore to tell people apart we must be able to identify subtle differences in their features. If you consider the similarities in appearance between some family members, this task can be very difficult indeed.

“It has been hypothesised that this task is so difficult that it can only be accomplished by primates, which have a large and complex brain. The fact that the human brain has a specialised region used for recognising human faces suggests that there may be something special about faces themselves. To test this idea, we wanted to determine if another animal with a smaller and simpler brain, and with no evolutionary need to recognise human faces, was still able to do so.”

The researchers found that fish, which lack the sophisticated visual cortex of primates, are nevertheless capable of discriminating one face from up to 44 new faces. The research provides evidence that fish have impressive visual discrimination abilities.

In the study, archerfish were presented with two images of human faces and trained to choose one of them by spitting water at them. The fish were then presented with the learned face and a series of new faces and were able to correctly choose the face they had initially learned to recognise. They were able to do this task even when more obvious features, such as head shape and colour, were removed from the images.

Dr Newport said: “Fish have a simpler brain than humans and entirely lack the section of the brain that humans use for recognising faces. Despite this, many fish demonstrate impressive visual behaviours and therefore make the perfect subjects to test whether simple brains can complete complicated tasks.

“The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognise human faces. Humans may have special facial recognition brain structures so that they can process a large number of faces very quickly or under a wide range of viewing conditions.”

Human facial recognition has previously been demonstrated in birds. However, unlike fish, they are now known to possess neocortex-like structures. Additionally, fish are unlikely to have evolved the ability to distinguish between human faces.

The study is published in the journal Scientific Reports.

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